Presentation on theme: "The Highest-Redshift Quasars and the End of Cosmic Dark Ages Xiaohui Fan Collaborators: Strauss,Schneider,Richards, Hennawi,Gunn,Becker,White,Rix,Pentericci,"— Presentation transcript:
The Highest-Redshift Quasars and the End of Cosmic Dark Ages Xiaohui Fan Collaborators: Strauss,Schneider,Richards, Hennawi,Gunn,Becker,White,Rix,Pentericci, Walter, Carilli,Cox,Bertoldi,Omont,Brandt, Vestergaard, Jiang, Diamond-Stanic, et al. SDSS collaboration
questions 1.How to discover the most distant quasars in the Universe? 2.When did the earliest quasars and super-massive black holes appear in the Universe? 3.How were the “cosmic dark ages” ended by the first generation of galaxies and quasars?
End of cosmic dark ages Hot Big Bang Cosmic Dark Ages: no light no star, no quasar, universe dark; IGM atomic (neutral) and opaque to UV First light: the first galaxies and quasars in the universe End of cosmic dark ages: Universe lit up and heated up Dark --> light Neutral --> ionized (reionization) today Courtesy: G. Djorgovski
Why Distant Quasars? –Existence of supermassive black holes (BHs) at the end of cosmic dark ages –BH accretion history in the Universe? –Relation of BH growth and galaxy evolution Evolution of Quasar Density molecular CO emission from z=6.42 quasar Detection of Gunn-Peterson Trough – Probing the cosmic reionization
The end of dark ages: Movie Courtesy of N. Gnedin
How to find the earliest and most distant quasars? They are extremely rare –One per 500 sq. deg at z>6 (M<-27) –Require the largest survey of the sky to catch them –Search for “red”, i-dropout objects in the Sloan Digital Sky Survey They are faint at high-redshift –Require deep follow-up spectroscopic observations –SDSS i-dropout survey: Candidate selection from SDSS Fellow-up observations mainly on four work-horse telescopes: APO 3.5m; KPNO 4-m; MMT; Keck
The Highest Redshift Quasars and Galaxies SDSS i-dropout Survey: –Completed in June 2006: 7600 deg 2 at z AB <20 –Twenty-five luminous quasars at z>5.7 –z max =6.42 –Cosmic age ~ 800 Myr –The first 6-7% of cosmic history Dropout and Ly emission galaxies –z spec < 6.6 –z phot ~ 7 - 8 GRBs –050904 z=6.30
Massive black holes in early universe From SDSS i-dropout survey –Density declines by a factor of ~40 from between z~2.5 and z~6 Cosmological implication –M BH ~10 9-10 M sun –M halo ~ 10 12-13 M sun –rare, 5-6 sigma peaks at z~6 (density of 1 per Gpc 3) Assembly of massive dark matter halo environment? Assembly of supermassive BHs? Fan et al. 2004
How fast can a black hole grow? Quasars shine by converting potential energy to radiative energy when accreting gas: –Radiative efficiency of ~10% Quasar maximum accretion rate is limited by the presence of radiation pressure (Eddington limit) –At maximum accretion, e-folding timescale of quasar growth is ~40 million years Earliest quasars likely grew from “seed” black holes resulted from stellar collapse –Seed mass ~10 - 100 M_sun To grow a billion solar mass BH needs about 20 e-folding time -> ~ 800 million years, non-stop The age of the universe at z~6 is ~800 million years –Barely enough time for quasars to grow, even non-stop from the big bang???
Surprise 1… How did black holes grow so quickly in the first billion years of the cosmic history? –New (astro)physical processes? Direct formation of intermediate mass BH? Much more efficient accretion? –How are the earliest quasars related to the earliest galaxies?
NV OI SiIV Ly a Ly a forest Rapid chemical enrichment in quasar vicinity High-z quasars and their environments mature early on The Lack of Evolution in Quasar Intrinsic Spectral Properties
Submm and CO observation of z=6.42 quasar: Co-formation of earliest BH and galaxies Strong submm source: –Dust T: 50K –Dust mass: 7x10 8 M sun –Star-formation rate of ~2000 M/yr Strong CO source –T kin ~ 100K –Gas mass: 2x10 10 M sun –gas, dust properties similar to those of the brightest local starburst galaxies Bertoldi et al.
High-resolution CO Observation of z=6.42 Quasar Spatial Distribution –Radius ~ 2 kpc –Two peaks separated by 1.7 kpc Velocity Distribution –CO line width of 280 km/s –Dynamical mass within central 2 kpc: ~ 10 10 M_sun –Total bulge mass ~ 10 11 M_sun < M-sigma prediction Small, star-forming galaxy hosted over-sized BH BH formed before complete galaxy assembly? Walter et al. 2004 1 kpc VLA CO 3—2 map 60 km/s Channel Maps
Lineless quasars: radio quiet BL Lac or quasars with no BLR? No emission line, radio-quiet quasars at z>4 –~1% of high-z quasars –No obvious low-z counterparts –No BL Lac signature –A separate population of quasars? Fan et al. 2006 Ly distribution Diamond-Stanic et al. 2006 Lineless Quasars: EW(Ly )<10 Log EW (Ly )
Surprise II… The spectra of these earliest quasars look almost identical to those in the local universe –No evolution in spectral properties? –Mature quasars in a very young universe? –Black holes grew earlier in the universe?
reionization Gunn-Peterson (1965) effect deep HI absorption in high-z quasar spectrum prior to the end of reionization
The Universe transforming from opaque to transparent at the end of cosmic dark ages transparent opaque
Implications of Complete Gunn-Peterson Trough G-P optical depth at z~6: –Small neutral fraction needed for complete G-P trough –By itself not indication that the object is beyond the reionization epoch The evolution of G-P optical depth: –Tracking the evolution of UV background and neutral fraction of the IGM –Probe the ending of reionization
The End of Reionization Optical depth evolution accelerated –z<5.7: ~ (1+z) 4.5 –z>5.7: ~ (1+z) >11 (1+z) 4.5 (1+z) 11 Evolution of Ionization State: Neutral fraction increases by >15 Mean-free-path of UV photons decreases by >10 Large variation in the IGM properties z~6 marks the end of cosmic reionization Neutral fraction
Three stages Pre-overlap Overlap Post-overlap From Haiman & Loeb
What’s Next Faint quasar survey at z~6: –In deep SDSS stripe –Additional 10 - 30 quasars at 1-2 mag fainter –Uses the upgraded MMT red channel -> new red-sensitive deep depletion CCD –Measures quasar luminosity function at z~6 –Probes the inhomogeneity of reionization by multiple line of sight Future IR-based quasars surveys: –On UKIRT, VISTA –Allows detection at z~8-9 JWST: –Probing the first light at z>10